The overall goal of the proposed research is to develop a three-dimensional (3-D) deterministic radiation transport code based on discrete-ordinates transport methods to obtain computationally fast and highly accurate dose distributions for Radiation Treatment Planning (RTP). It is anticipated that deterministic methods can produce dose distributions as accurate as Monte Carlo (MC) codes, but may be sufficiently faster to be incorporated into optimization calculations. The goal of the R21 phase is to show that electron transport with existing discrete-ordinates transport codes is possible and to examine the accuracy of the resulting dose distributions in realistic anatomic models through comparison with results from well-established MC coupled electron-photon transport codes. In the R33 phase of the proposal, ORNL and its collaborators will create a specialized discrete ordinates software package that will include electron transport, optimized for voxel geometries.